Attention KX/KDX hybrid builders

[karlp]

I have searched on this topic and have not found exactly what I was looking for.... yet.

I have an '02 KDX and a '95 KX. I ride them both and sure do wish the KDX motor was in the KX. The KX geometry and weight are great, the motor is a handfull.

What holds me back from doing a hybrid is the swingarm issues. It looks like the KDX swingarm will bolt right up to the KX frame, if the KDX engine was in there.

Why have all of the hybrid builders I have seen opted to either mill the KDX engine case or cut the KX swingarm?

Am I missing something magical about the KX swingarm/rear suspension?

The KX swingarm is about an inch longer than the KDX swingarm. Apart from that it looks like everything alse would move over. I would have to use the KX shock and knuckle but probably a custom pull rod length.

Thanks in advance for any insight

_________________
'02 220 with '95 kx forks
'95 kx with KDX forks
KX100 for the wife
Husky 50 for the boy

 

[placelast]

I had a 1998 KX125 framed-based conversion. The KDX cases were machined to narrow them up to fit the KX swingarm. I don't have the details as the basic conversion was done by another; I did the enduro conversion.

Hope this helps.

 

[Wilky]

You have to do both..... and more. The KDX swing arm bolt has about a 2mm smaller diameter than the KX which make the KX frame and swing arm incomputable with the KDX bolt. Also the KDX engine is a little wider than the 125 so you will need to cut down the kx collars so the 200 will fit in there. You will also have to flatten out the clutch side of the kx frame a little so the clutch case doesn’t rub. The fuel tank will need to be heated and modified so the water outlet on the head doesn’t come in contact with it. I have made two hybrids, 1994 motor in a 92 kx125 and a 1990 motor in a 94 CR125 and I had to modify both motors by enlarging the swing arm hole from 15mm to 17mm (if my memory is correct) and cutting down the collars. The CR didn't need the frame mods but did require the fuel tank to modified a little.

A couple more things. On a post 94 KDX engine the head has a motor mount on the front and back. I believe you will have to remove the back motor mount on the head so it doesn’t hit the fuel tank when mounted in the kx125. You may also need to make some custom motor mounts for the front head mount and you will defiantly have to weld on new lower mounts to the frame.

Hope this helps.

Scott

 

[mark_england]

simple answer to this,, the kx swing arm is designed to work with the kx frame.

why make it more complicated for yourself... also you risk it becoming a ill handling dog.

 

[Green Hornet]

Fredette does the conversions also

 

[karlp]

Very good information
I was thinking that the KDX engine, swingarm, and bolt all move together over to the KX frame. The KX frame spacing measures the same as the KDX.

The possibility of an ill handling dog of a bike is what concerns me. The KX is a fine bike, the motor is a bit much. The KDX motor is fine, the handling ain't like the KX'es.

 

[mark_england]

Very good information
I was thinking that the KDX engine, swingarm, and bolt all move together over to the KX frame. The KX frame spacing measures the same as the KDX.

The possibility of an ill handling dog of a bike is what concerns me. The KX is a fine bike, the motor is a bit much. The KDX motor is fine, the handling ain't like the KX'es.

i built a kdx/kx for a friend,, turned out a lovely bike handled like a dream.

i liked it so much i decided to build myself one,, but built myself a yz200 instead,
using a yz125 chassis and a wr200 motor.

 

[timbuchanan]

Is it too hard to de-tune the kx so it isnt a handful?

It just seems like a lot of work to swap over an engine to a frame that wasnt exacly designed for it when you could just modify the original. This is not based on any real knowledge but just doesnt seem right.

So my question is how can you tame a kx to become more rideable?

 

[timbuchanan]

By the way thats a nice looking yz200 there mark

 

[karlp]

I suppose you can de tune the KX, but you can't make it a KDX 220 motor.

 

[timbuchanan]

I suppose you can de tune the KX, but you can't make it a KDX 220 motor.

Surly a smaller carb, flywheel weight and more restrictive exhaust would make it similar in nature and all are simple bolt on mods

 

[ebeck]

mark_england, I have a question about the exhaust and air box.
1) What air box did you use
2) Did you put the pipe on before you fabricated motor mounts or did you mount the engine as low as possible and then modified the pipe. Were you able to keep the pipe unodified?
3) KX or KDX radiators or does t make a difference. I assume KX as it goes with the frame.

One thing that concerns me about doing this is that if I dump the bike and damage the pipe, I would hate to have to fabricate on a new pipe every time.